Protein texturization

ABSTRACT

A bland protein product having a texture and mouth feel simulating animal meat is prepared from a dough-like mixture of proteinaceous material and water. The proteinaceous material can comprise relatively low protein content blends or even single ingredients such as soy flour. The process comprises continuously extruding the protein dough in the form of a relatively thin sheet of semi-rigid protein material into a first confined treating zone while simultaneously subjecting the thin sheet in the extrusion die to externally applied heat to texturize both surfaces of the sheet before it enters into the first confined zone. A stream of heated gas and condensables is introduced into the first confined zone to buoy up, flex and help propel the sheet of surface - texturized protein through the confined zone where additional texturization takes place. The sheet then is cut into segments by rotating longitudinal knife edges against a stationary straight edge and the segments are conveyed through a second confined zone where final texturizing takes place. Finally, the protein segments are passed through a suitable back pressure means at the end of the second confined zone, and recovered in usable form. Apparatus for performing this process is also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the treatment of untextured protein materialsto form a product possessing the fibrous texture and mouth feelproperties of animal meat.

2. Description of the Prior Art

The food industry has spent much effort over a span of many years andhas expended large sums of money in an attempt to utilize non-meatproteins, such as those derived from vegetables, as additives to orsubstitutes for animal meat products. It long has been recognized thatthe ever-increasing worldwide food shortage could be in material partobviated if only such relatively inexpensive materials could beconverted into products so closely approximating the naturally occurringfood material that public acceptance would be achieved. One of the majorroadblocks encountered by the industry has been the inability to impartthe natural and accustomed chewy, fibrous texture to vegetable proteinmaterials. Animal meat products inherently possess a texture giving thema definite "mouth feel" which is clearly recognized and stronglypreferred. Vegetable proteins in their natural state generally take theform of amorphous powders which, despite their unquestioned nutritivevalue, possess mouth feel characteristics wholly unacceptable to theconsumer as a meat substitute. Moreover, vegetable proteins normally arecharacterized by objectionable "beany" flavors which the industry hasbeen unable to remove or mask.

In recent years a number of processes and apparatus have been developedfor treating vegetable protein material to produce a bland texturizedproduct. None of these processes, however, has achieved any substantivemeasure of commercial success.

The first generation of these prior art techniques involved the wetspinning process disclosed in Boyer, U.S. Pat. No. 2,730,447. Thisprocess produces a fibrous product by extruding a plurality of finestreams of an aqueous solution of protein into a chemical coagulatingbath. The protein coagulates into fine fibers which are collectedtogether and treated to form an adible textured protein product. The wetspinning process suffers from a number of drawbacks in addition to itsgeneral failure to produce an adequately textured product as discussedabove. The equipment employed to perform this process is extremelysophisticated for the food industry and represents a very high initialcost problem. Adding further to the economic infeasibility of theproduct produced by the wet spinning process is the expensive startingmaterials which must be employed. Moreover, product uniformity isdifficult to achieve due to the general complexity of the process andthe numerous parameter control problems presented.

The second generation technique advanced in this area is the extrusioncooking process disclosed in Atkinson, U.S. Pat. No. 3,488,770 in whicha protein mass is subjected to severe physical working at an elevatedtemperature and thereafter extruded at an elevated temperature andpressure through an orifice into a medium of lower pressure andtemperature. This process suffers from high equipment costs and isextremely energy intensive due to the extreme temperature and pressurerequirements. In addition, the product produced by extrusion cooking hasa very low denisty which swells up in water to give a "spongy" texture.Moreover, the product contains objectionable flavor notes in addition tothe "beany" flavor originally present in the starting materials whichare apparently imparted to the product by the severe processing steps.Other patents demonstrating the current state of the art in respect tothe extrusion texturing approach inlude Hale, U.S. Pat. No. 3,447,.929;Jenkins, U.S. Pat. No. 3,496,858; Anker, U.S. Pat. No. 3,684,522;Strommer, U.S. Pat. No. 3,778,522; Lang, U.S. Pat. No. 3,800,053;Atkinson, U.S. Pat. No. 3,812,267; and Yang, U.S. Pat. No. 3,814,823.

The third generation of development in the protein texturizationinvolves the use of steam as the texturizing medium. Exemplary of thisapproach are Strommer, U.S. Pat. Nos. 3,754,926 and 3,863,019 whichtreat either finely divided protein particles or slurries with steam andHeusdens U.S. Pat. No. Re. 28,091 which employs a steam treatment ofprotein slurry following complex hydration steps. Products produced bythese processes also possess the general problems of poor texture andflavor discussed above. In addition, the product has low densityproblems similar to the second generation extrusion cooked products inthat on hydration they tend to be very soft. The product is alsoextremely friable.

Other attempted solutions by the art include cooking and shaping of aprotein dough disclosed in McAnelly, U.S. Pat. No. 3,142,571, and theheat coagulation of undenatured protein disclosed in Rusoff, U.S. Pat.No. Re. 27,790.

Notwithstanding the veritable plethora of prior art attempts tosatisfactorily texturize vegetable proteins -- no one to date has madeany really substantial progress toward the desired goal. The presentabsence from the market of any commercially accepted consumer productsbased on vegetable protein demonstrates clearly that the problemsinvolved simply have not been solved. Indeed, those meat analog productswhich have found their way to the supermarket shelves generally havebeen met with little or no consumer acceptance and have generally beenwithdrawn. Especially in the United States, where consumer preferencesrather than nutritional values often dictate the fate of food products,a successful texturized vegetable protein material simply must possesstaste and mouth feel characteristics similar to natural meat. Inaddition, the prior art processes generally have employed such complexapparatus and procedures that initial equipment and operating costs havemade protein analog products economically unattractive to manufacturers,despite the relatively inexpensive nature of the raw product.

Given the ever-increasing fears of worldwide famine and the diminishingavailability of animal meat protein products, it is clear that aninexpensive, consumer-acceptable, high protein food product based ontexturized vegetable proteins is urgently needed.

BRIEF SUMMARY OF THE INVENTION

It is the object of the present invention to provide a process andapparatus for texturizing protein which fulfills the need left by theprior art texturizing processes.

More specifically, it is an object of the present invention to provide aprocess and apparatus for producing thin discrete segments of relativelydense protein material having a fibrous texture simulating that ofnatural meat.

It is a further object of the present invention to provide a process andapparatus which will produce a bland flavored protein product.

Another object of the present invention is to provide a process andapparatus which will produce a retort stable protein product.

It is also an object of this invention to provide a texturizing processand apparatus which will produce such a product at a much lower cost dueto lower initial equipment costs and lower energy requirements.

It is also an object of the present invention to provide a high qualitytexturized protein product from relatively inexpensive, low proteinstarting materials.

Accordingly, the present invention comprises a method for producing arelatively dense texturized protein product with a unidirectionallaminated surface structure comprising mixing untextured proteinmaterial and water to form a protein dough, said dough containing fromabout 60 to 73% solids; advancing said dough to an extrusion die at atemperature below that at which texturization takes place; continuouslyextruding said dough in the form of a thin sheet of protein materialthrough said extrusion die while simultaneously texturizing bothsurfaces of said thin sheet as it passes through said die by applyingheat to both surfaces of said sheet from a source external the diewalls; passing said extruded sheet in unbroken form directly into afirst confined treating zone while simultaneously introducing a heatedgaseous stream into said first confined treating zone, whereby saidunbroken extruded sheet is buoyed up and flexed by said gaseous streamand said unbroken extruded sheet is further texturized as a result ofthe extended exposure to the conditions in said first confined zone;cutting said unbroken extruded sheet into segments as it reaches the endof said first confined treating zone; conveying said cut segmentsthrough a second confined treating zone communicating with said firstconfined treating zone, whereby the protein segments are furthertexturized; passing said protein segments through means for maintainingback pressure disposed at the discharge end of said second confinedtreating zone; and recovering the texturized protein segments.

The present invention further provides apparatus for texturing proteinmaterial comprising die means for extruding a continuous, relativelythin sheet of semi-rigid protein material; means for externally applyingheat to both surfaces of said thin sheet as it passes through said diemeans to effect surface texturization of said thin sheet; means defininga first confined treating zone communicating with said die means; meansfor introducing a heated gaseous stream into said first confined zone;means for cutting said extruded sheet into segments disposed at thedischarge end of said first confined treating zone; means defining asecond confined treating zone communicating with said first confinedtreating zone; and means for recovering said texturized proteinmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents a schematic of one embodiment of the apparatus of thepresent invention.

FIG. 2 is a sectional view taken along lines 2--2 showing the slittingmeans at the discharge from the die assembly.

FIG. 3 is a sectional view taken along lines 3--3 showing the cuttingmeans at the discharge end of the first confined treating zone.

FIG. 4 is a photomicrograph of a section of the product produced by thepresent invention, observed at 50X.

FIG. 5 represents a series of photomicrographs of an interior section ofthe product produced by the present invention; 5a is at 25×; 5b at 50×;5c at 100×; 5d at 300×; 5e at 500×; 5f at 1000×; and 5g at 1500×.

FIG. 6 represents a series of photomicrographs of an exterior section;6a is at 50×; 6b is at 100×; 6c at 300×; 6d at 500×; 6e at 1000×; and 6fat 1500×.

FIG. 7 represents a series of photomicrographs of the product of theprior art extrusion cooking process; 7a is taken at 50×; 7b at 100×; 7cat 300×; 7d at 500×; 7e at 1000×; and 7f at 1500×.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a process and apparatus fortexturizing protein material. The term texturizing as used herein andwidely understood in the art refers to the process of changing globularamorphous particles of protein into fibrous continuous phase proteinmaterial with structural identity.

The term retort stable as used herein refers to a product which keepsits structural integrity after treatment at elevated temperature andpressure. In the typical retort processing test about 1 part texturizedprotein is mixed with 10 parts of a 1% salt solution and sealed in acan. The can then is placed in a retort and subjected to a temperatureof 250° F. and a pressure of 15 psig for about 60 minutes. The abilityof a retorted product to maintain its structural integrity and bitecharacteristics can be tested by placing the product between the thumband forefinger and subjecting the product to shear forces. A retortstable product will not disintegrate with moderate finger pressure. Aproduct with poor retort ability will feel mushy and will fall apartwhen subjected to moderate shear forces.

Protein material employed in the process of the present invention shouldcontain at least about 40% protein on a dry weight basis. Of primaryinterest are vegetable protein materials derived from soybean. Soyproteins can take the form of soy flour, soy concentrate, soy isolatesor mixtures thereof. The process of the present invention is especiallywell suited to texturizing low protein materials such as soy flour.Other oilseed materials such as peanut, cottonseed, and sesame seed mayalso be employed. Other known protein materials such as those derivedfrom wheat, milk, egg, single cell or leaf proteins and the like may betexturized according to the process of the present invention. Proteinmaterial employed should be viable, i.e., have a PDI (ProteinDispersability Index) in the range of from about 40 to about 90%.

Other protein sources suitable for the practice of the present inventioninclude natural meat products. When texturizing meat proteins, thestarting material employed should consist of a mixture of meat and aprotein binder. Meat proteins may comprise meat scraps or piecespossessing poor textural qualities such as mechanically deboned chicken,beef, seafood, etc. or blends of the foregoing. Suitable protein bindersinclude vegetable proteins such as soy protein or other known proteinssuch as those derived from wheat, yeast, milk, egg, etc. In general,mixtures containing up to about 80% comminuted meat may be texturizedaccording to the process of the present invention.

In accordance with the preferred embodiment of the process of thepresent invention the protein material described above is first mixedwith water to form a protein dough or paste containing from about 60 toabout 73% solids. This pasty or dough-like mixture then is advanced in apassive screw feeding means. In this feed zone the product may bepreheated to a relatively low temperature in the range of about 110 upto about 150° F. It will be recognized that this is a temperature belowwhich texturization will occur. The screw feed should be of the low worktype which serves mainly to advance the protein dough rather thansubjecting it to severe physical working, and typically is operated atless than 50 RPMs and preferably between about 20 to 30 RPMs. Bestresults are achieved at about 25 RPMs.

Protein dough from the screw feed chamber then is forced under pressurethrough an extrusion die assembly which forms the protein into a thinsheet-like product. Applicants have found that an extruded proteinproduct will possess better overall textural qualities if aunidirectional laminar texturization is imparted to both surfaces of theprotein sheet while it is still in the die assembly. Surfacetexturization of the protein sheet while it is still in the die assemblyhas been found to build in certain unique textural characteristics tothe protein structure such as retort stability, greater density andfirmer bite identity.

Surface texturization as used herein is accomplished by applyingexternal heat to both surfaces of the thin protein sheet as it passesthrough the die assembly. As the protein sheet passes through the die,it should contact the heated die surfaces for a time sufficient totexturize the surfaces of the protein sheet. The residence time in thedie can be controlled by varying the product feed rate and/or byincreasing the length of the die assembly. Generally, residence times offrom about 0.3 minutes up to about 1 minute or more are satisfactory toachieve the requisite degree of surface texturization. The preferredresidence time is about 0.5 minutes. The upper limit on die residencetime should be less than the time at which thermal degradation begins.

The protein sheet formed in the die should be relatively thin to achievethe overall enhanced properties of the present invention. Satisfactoryresults have been achieved with sheet thickness of up to about 1/2 inch.The preferred sheet thickness is about 3/16 inch. The sheet thicknessshould not be so great as to have a significant adverse effect on thefinal product.

As used herein, the term "sheet" is intended to include (1) a flatproduct with length and width dimensions much greater than itsthickness, like a sheet of paper; and (2) a product in which a sheet asdefined above is not all in one plane, e.g., a tubular sheet formed froma flat sheet as in (1). When referring to "both" sides or surfaces of atubular sheet, the inner and outer surfaces are intended.

In the preferred embodiment the die assembly produces a thin tubularsheet of protein. The term "tubular" as used throughout thespecification and claims refers to shapes other than cylindrical tubes,such as square or triangular tubes. In the preferred embodiment,however, the tubular extrudate forms a right circular cylinder ofprotein dough.

Extrusion pressures developed at the orifice in the range of about 1000to about 2000 psig are suitable in the practice of the presentinvention. The temperatures developed at the extrusion die are generallyin the range of from about 150 to about 320° F.

The thin protein sheet having the above described textured surface isextruded directly into a first confined treating zone. In this firstzone, additional texturization of the unbroken protein sheet is effectedby the action of heat and pressure from the separately introducedflowing gaseous steam. The gaseous stream causes the sheet to buoy up,flex and helps convey the sheet around the inner die support. Theextruded sheets are retained in the flowing stream of heated gas in thefirst confined zone for an extended period of time, e.g., for up to a11/2 minutes or more and this results in further texturizing. Extendedresidency times of up to about 0.75 min are preferred. During thisperiod the flowing gas is extremely effective to impart texturedqualities to the protein product. Moreover, this extended holding periodallows a high degree of texturization to be achieved without employingan extremely long confined treating zone.

Along with the extruding forces, gravity and the gaseous stream help theprotein sheet to flow into the segment cutting area disposed at thedischarge end of the first confined zone. The protein sheet is cut intosegments by a cutting assembly affixed to the rotating screw of a screwconveyor which conveys the segments through a second confined treatingzone.

When the thin extruded sheet of protein is tubular in shape, it ispreferred to longitudinally slit the tube into a plurality of individualarcuate sheets as the tube leaves the die assembly. Each of thesearcuate sheets then is subjected to the gas flow and cut off in themanner described above.

In the preferred embodiment the gaseous stream is high pressure steam.Generally, any steam pressure below that which will cause the extrudedprotein sheet to break off before it reaches the cutting means, may beemployed. In practice, it has been found that pressures of about 80 to150 psig are suitable to accomplish this result. Best results areachieved when employing pressures in the range of from about 110 toabout 120 psig. The gaseous stream may be introduced into the firstconfined treating zone in any manner which avoids premature breaking offof the protein sheet.

After the discrete segments of textured protein have been cut off fromthe proteins sheets, the screw conveyor forwards the segments throughthe second confined treating zone through which the heated gaseousstream introduced into the first confined treating zone also flows. Inthis second confined treating zone the elevated temperature, pressureand turbulence of the gas flow imparts further texture to the proteinpieces and volatilizes objectionable flavor compounds.

Generally, temperatures in both the first and second confined treatmentzones of up to about 350° F. are suitable to achieve texturization withbest results achieved in the range of 310 to 350° F. Pressure in saidconfined treatment zones is regulated by a back pressure maintainingmeans at the discharge end of the second confined zone. Back pressuresof up to about 105 psig measured at the exit port of the second confinedzone should be maintained in the zones. Preferably, the back pressure iskept in the range of 60 to 105 psig. After passing through the backpressure maintaining means the protein segments can be recovered in anyknown manner.

One embodiment of the apparatus of the present invention now will bedescribed by reference to FIG. 1. A mixture of protein to be texturizedand water is formed in any suitable mixing means 1. The dough-likemixture from the mixing means is discharged into a screw feed chamber 2.The screw feed chamber may be unheated over most of its length andserves only to forward the dough to the extrusion die. As the proteindough nears the extrusion die some external heat may be applied by steamor hot water jackets 3 or the like.

Communicating with the screw feed chamber is an elongated die assembly 4which is effective to extrude a thin sheet of semi-rigid protein dough.The die assembly of the preferred embodiment comprises twoconcentrically disposed cylindrical surfaces defining a tubularextrusion orifice. The product produced by such a die assembly is acontinuous tube of protein material. As indicated above, the preferredshape of the extrusion orifice defined by the die assembly is a rightcircular cylinder, although other shapes may be employed.

In order to achieve a product with high textural qualities the dieassembly should be equipped with provision for supplying external heatto both sides of the protein sheet. This externally supplied heat cantake the form of steam jackets. When the extrudate is a tubular sheet,heat must be applied to both the inner and outer surface by steamcontaining areas 5 and 6 respectively. The requisite degree oftexturization is not achieved when only one side of the sheet is heated.

As the thin tubular sheet leaves the die assembly, it is longitudinallysliced into a plurality of continuous arcuate sheets by a plurality ofknife edge slitting means 7, as best shown in FIG. 2.

Communicating with the die-slitter assembly is a first confined treatingzone 8. As the protein sheets enter this treating zone, a stream ofheated gas is also introduced into the zone. This preferably isaccomplished by employing the steam from die heating chamber 5 which isinside the tubular extrudate.

In the first confined treating zone 8 the protein material is subjectedto the action of heat and pressure from the turbulent gas flow.Preferably, this confined treatment zone takes the form of an elongatedtube or chamber. The dimensions of this tube are not critical. Inpractice, tube lengths of about six to ten feet generally providesuitable retention times although longer or shorter tubes may beemployed satisfactorily.

At the discharge end of said first confined zone the unbroken proteinsheets enter a cutting zone where they are cut into individual segments.Cutting means 9, as best seen in FIG. 3 comprises a stationary cuttingedge 10 mounted at the entrance to a second confined zone 11, and aplurality of rotating cutting edges 12, mounted on a screw conveyor 13in the second confined treating zone.

At the discharge end of the second confined treating zone is a backpressure maintaining means 14. This back pressure means can comprise,for example, a spring loaded valve, a rotary valve, or a rotary letdownpump. In general, any device which allows the product to exit theconfined zone while maintaining a back pressure upstream may beemployed. Suitable back pressure devices in the rotary letdown pumpcategory include the CP-6 made by Creamery Package Co., Inc., and ModelR2-4PB Foster Food Pump made by Foster Pump Works. The product issuingfrom the back pressure means may be subjected to recovery by any knownmeans. Since the product is essentially dry, it is only necessary toforward the steam/protein mixture to a zone where the steam can bevented off.

The product produced by the process of the present invention comprisessheet-like segments of protein material having structural and eatingproperties similar to animal meat products.

This product consists of two discrete regions. A cross section of aportion of the extruded protein sheet of the present invention is shownin the photomicrograph of FIG. 4. At the surface of the sheet, shown atthe right of the picture, is a layer of dense fibrous protein materialoriented in one direction. This surface orientation is achieved by thespecial surface texturizing performed in the extrusion die according tothe present invention. The interior portion of the sheet-like product ofthe present invention is a dense protein matrix containing an openspherical cell development.

The interior porous structure of this product is best shown in theseries of photomicrographs in FIG. 5. This unique system of sphericalvoids surrounded by a dense fibrous matrix provides randomly spacedshear points which give way upon chewing to provide bite and mouth feelcharacteristics which simulate normal meat products.

The laminar surface texturization of the product of the presentinvention is best shown in the series of photomicrographs which make upFIG. 6. This dense fibrous skin is formed on both sides of the productwhere the sheet touches the heated die surfaces.

By way of contrast, the product produced by the prior art extrusioncooking process described above is shown in FIG. 7. This productexhibits a structure comprising layers of protein separated by anelongated oval void system. Note also that the matrix is not very dense.

Furthermore, the product of the present invention is free fromobjectionable flavor notes which in themselves often made prior artproducts unacceptable to humans. The severe working, temperature, andpressure conditions present in the prior art extrusion cooking processesare believed to generate certain off flavors not produced in therelatively passive treatment of the present invention.

The severe conditions of the prior art processes are also believed toadversely affect the color and nutritional value of the finishedproduct. The product produced according to the present inventionpossesses excellent color and nutritional stability. Another advantageachieved by the process and apparatus of the present invention lies inthe retort stability of the product. Due to the unique structureimparted by the combination of surface texturizing in the die followedby steam texturizing in the confined zone, the protein product formed inaccordance with this invention may be processed by conventional foodpreparation techniques without thermal degradation of its physical ororganoleptic properties.

Products produced by the process of the present invention find utilityin a number of food processing fields. These texturized protein productsmay be cut into portions suitable for direct incorporation into cannedor frozen foods. The texturized products may also be employed as afiller or extender in ground meat products. It is also possible toproduce fabricated nutrients from the protein material producedaccording to the present invention.

The process of the present invention is also useful to provide upgradedor restructured natural meat products. Meat scraps or by-products withlittle or no food value (due to their poor structural characteristics)can be texturized according to the process of the present invention toprovide chicken, crabmeat, etc. cubes with good texture and mouth feel.

The following specific examples are intended to illustrate more fullythe nature of the present invention without acting as a limitation onits scope.

EXAMPLE 1

Over 5,000 pounds of the product of the present invention were producedat approximately 360 pounds per hour of finished product at less than10% moisture with an input dough moisture of approximately 30% at 468PPH. Soy flour obtained from Central Soya, Chemurgy Division known asSoyafluff 200W with a minimum of 50% protein of which 60-70% of thisprotein was watersoluble was used. Dough thickness in the die was 0.187inches which caused up to 2,000 psig dough pressure in the die. Lowthroughput product rate and over texturizing and burnt flavor in theproduct was observed. Steam pressure in area 5 (FIG. 1) was 75 to 78psig. Steam pressure in area 6 (FIG. 1) was 70 to 73 psig. Steampressure in areas 8 & 11 (FIG. 1) were 70 to 73 psig. Producttemperature was maintained 315 to 316° F. in the pressure zones. Theretention screw rotated at 68 to 52 RPM. The rotary valve rotated at 91to 70 RPM, as the valve and screw are driven by the same motor the valvespeed will be 1.35 times screw speed. The textured material out of therotary valve flashed when discharged to atmospheric pressure. The gaseswere drawn off with an exhaust system and the product was conveyed to adryer. An inlet temperature of the dryer was 308 to 320° F. The driedmaterial was then ground to a practical size 100% through a U.S.S.6-mesh screen and 53 to 60% retained on a U.S.S. 20-mesh screen. Thisgrind size will vary when different grinder screens and speeds are used.The ground product was conveyed by cooled air to reduce the temperatureof the product below 100° F. for bagging. The inside diameter of theouter die was approximately 8.0 inches the inner die outside diametercan be machined to a diameter to obtain the desired dough thickness. Thelength of the die dough heating section is 24 inches long. Thelongitudinal slitter makes 24 cuts, resulting in the product strandshaving a width of approximately one inch. The strands stayed intactuntil they extend down to the screw conveyor knife area where they werecut within an arbitrary length according to the screw speed andextrusion rate. This cut length can be varied from 1/2 inch to 3 incheslong and was then conveyed under pressure to the discharge valveapproximately 48 inches where it was discharged on to a conveyor belt atatmospheric pressure, conveyed to the dryer, grinding, and baggingsystem.

EXAMPLE 2

In this example the dough thickness was increased to 0.250 inches thusincreasing the product die rate to 780 pounds per hour, reduced theproduct pressure in the die to 1,300 psig and maintaining all otherconditions as given in Example #1. The resulting product was found topossess excellent retort stability plus good texture and flavorcharacteristics.

EXAMPLE 3

In another example the dough moisture was increased to 33.6% H₂ O with aresulting decrease in the product die pressure to 1,150 psig with theproduct rate decreasing from 780 to 624 pounds per hour. Soyafluff 200Wwas used. The steam pressure in area 5, 6, 8 & 11 (FIG. 1) was increasedto 80 psig each to maintain a 320° F. product temperature in thepressure zones. The oven temperature was decreased to 300° F.,maintaining the product moisture below 10% moisture. A chunk productresembling sliced meat was produced which also exhibited good retortstability and quality.

EXAMPLE 4

In this example the dough thickness was increased to 0.281 inches in thedie. The average dough moisture in the die was 32.0% H₂ O whichincreased the die product throughput rate to 1,237 PPH and reduced thedie pressure to 1,000 psig. Soyafluff 200W was also used. The producttemperature in the pressure zones was 335° F. with the steam pressure inthe zones at 105 psig. The finished product moisture was less than 10%H₂ O and the oven temperature range was reduced to 275 to 280° F.Satisfactory textured and flavored product was obtained.

While certain specific embodiments of the invention have been describedwith particularity herein, it should be recognized that variousmodifications thereof will occur to those skilled in the art. Therefore,the scope of the invention is to be limited solely by the scope of theclaims appended hereto.

We claim:
 1. A method for producing a relatively dense texturizedprotein product with a unidirectional laminated surface structurecomprising:(a) mixing untextured protein material and water to form aprotein dough, said dough containing from about 60 to about 73% solids;(b) advancing said dough to an extrusion die at a temperature below thatat which texturization takes place; (c) continuously extruding saiddough in the form of a thin sheet of protein material through saidextrusion die while simultaneously texturizing both surfaces of saidthin sheet as it passes through said die by applying heat to bothsurfaces of said sheet from a source external the die walls, saidexternal heat source supplying sufficient heat to texturize the proteinat both surfaces of said sheet; (d) passing said surface-texturized,extruded sheet in unbroken form from the die directly into a firstconfined treating zone while simultaneously introducing a heated gaseousstream into said first confined treating zone, and further texturizingsaid unbroken sheet by extended contact with said heated gaseous stream,said heated gaseous stream being at a pressure and temperaturesufficient to partially texturize the protein in said surface-texturizedunbroken sheet, where said unbroken extruded sheet is buoyed up by saidgaseous stream such that it is conveyed over the die into the firstconfined treating zone; (e) cutting said unbroken extruded sheet intosegments as it reaches the end of said first confined treating zone; (f)mechanically conveying said cut segments through a second confinedtreating zone communicating with said first confined treating zone, andfurther texturizing said segments by continued contact with said heatedgaseous stream introduced into said first confined treating zone, saidheated gaseous stream being at a pressure and temperature, as it flowsthrough said second confined zone, sufficient to texturize the remaininguntexturized protein in said segments; (g) passing said protein segmentsthrough means for maintaining back pressure disposed at the dischargeend of said second confined treating zone; and (h) recovering thetexturized protein segments.
 2. The method of claim 1 wherein saidprotein material comprises at least about 40% protein on a solids basis.3. The method of claim 1 wherein said protein material comprises soyflour having a protein content of about 50% on a solids basis.
 4. Themethod of claim 1 wherein said protein dough is advanced to saidextrusion die by a low-work screw feeder.
 5. The method of claim 4wherein said protein dough is preheated to a temperature in the range ofabout 110 up to about 150° F. in said screw feeder.
 6. The method ofclaim 1 wherein heat is applied to both surfaces of said sheet by steamjackets.
 7. The method of claim 1 wherein said thin sheet of proteinmaterial is heated to a temperature of from about 150° F. to about 320°F. as it is being extruded.
 8. The method of claim 1 wherein said thinsheet of protein material is extruded at a pressure of about 1000 to2000 psig.
 9. The method of claim 1 wherein said extruded thin sheet istubular in shape and further comprising the step of longitudinallyslitting said tubular sheet into a plurality of continuous arcuatesheets as said tubular sheet enters said first confined treatment zone.10. The method of claim 9 wherein said tubular sheet comprises a rightcircular cylinder.
 11. The method of claim 1 wherein said gaseous streamis steam.
 12. The method of claim 11 wherein said steam is introducedinto said first confined treating zone at a pressure of about 80 toabout 150 psig.
 13. The method of claim 11 wherein said steam isintroduced into said first confined treating zone at a pressure of about110 to about 120 psig.
 14. The method of claim 1 wherein said first andsecond confined treating zones are maintained at a temperature of about310 to 350° F.
 15. The method of claim 1 wherein said first and secondconfined treating zones are maintained at a temperature of 310° F. 16.The method of claim 1 wherein the back pressure as measured at thedischarge end of said second confined treating zone is maintained atfrom about 60 to about 105 psig.